This invention relates to a geomechanical probe intended to be introduced into a drilling well for conveying fluid into the well and measuring various fracture parameters therein.
Particularly when an underground reservoir in line with a well is to be fractured, it is desirable to be able to forecast the main geometrical and hydraulic characteristics of the fracture that a particular type of treatment will induce, e.g. the maximum extent of the fracture; the number of different geological strata passed through; the azimuth of the plane containing the fracture; the limitation of the fracture at the wall and roof of the reservoir or, on the contrary, two superimposed deposits made to communicate with one another, etc.
To obtain this information, it is possible to use a digital simulator capable of modelling the behaviour of the injected fluid and the fractured rocks, taking into account all the conditions at the limits. However, this simulator can only provide reliable results if the correct data is entered into it. One of the most difficult parameters to measure is the in situ stress tensor, which largely governs the azimuth of the fracture, the confinement of the fracture by the walls of the reservoir and the speed of percolation of the fracturing fluid into the rock.
Although measurement of certain parameters can be made in the laboratory on rock samples obtained by core sampling, it is very important to supplement them with measurements obtained in situ by means of a probe lowered into the well. Comparisons between the two types of measurement can give valuable information particularly about the existence of fissures in situ. As regards the stress tensor, it may be possible to ascertain it from core-drilled rock samples because these samples retain the memory of the stresses to which they have been subjected, but this method of determination is still only at the research stage.
It would therefore be very useful to be able to carry out accurate measurements in situ by means of a probe lowered into a drilling well.
The devices proposed hitherto are very difficult or even impossible to produce and do not give sufficiently accurate information.